"C:\Qt\Tools\mingw491_32\bin..\libexec\gcc\i686-w64-mingw32\4.9.1\liblto_plugin-0.dll"
There's a missing \ after bin. Is that the output you're getting or is it an output -> forum transfer mistake?

The internet wisdom suggest two problems with the lto plugin in MinGW: one - it doesn't like spaces in paths. Does your project live in such location? A longshot but there's also a bug report on packaging of some versions of MinGW where they would add a 64bit plugin to a 32 bit compiler. Can you share some bittness info of your build and OS? In any case a workaround is to remove the -flto from the compiler command line so you might try that.

\bin..\ - this goes down the tree terminating in the bin folder; then goes back up a directory and finds libexec then back down to liblto_plugin-0.dll which is there. You probably already see that - just thought I would verify.

This is a copy and paste -- no transfer error. OS Win 8.1 current on updates, 32gb ram, 64 bit sys. If you suggest that I do the workaround might need a few instructions. Also, I am not aware of any whitespaces. Fresh install of QT and Qt Creator. Could reinstall and see if the problem goes away (sorry abt the magical thinking). Interestingly when I install it never makes a shortcut for me.

Oddly the first few times I ran this it would work. I don't know what's changed since.Would a direct include path to the location be helpful?